American Machinist

Raw grinding: today's grinders make big cuts without forfeiting accuracy or precision. (Grinding).

Don't believe the rumors that hard turning and other advanced machining processes are crowding out grinding. Technological advancements have not only improved grinding's accuracy and precision but have also increased its metal-removal rates tremendously. For instance, some of today's grinders can hog out more than 8 mm of material within 5 sec--at a rate of 160 m/sec--from raw cast iron crankshafts in an as-cast condition (green grinding). This is done without sacrificing accuracy or precision.

Technologies that make green grinding possible on crankshafts are also spreading to other part applications. Automakers are now testing modern grinders for roughing camlobes from steel barstock blanks with machined grooves that delineate the main journal and lobe diameters. So rather than losing ground to other operations, grinding directly from raw stock has the potential to compete with turn-broaching, milling, and other large-chip machining processes.

Although advancements in grinding technology are redefining the rules-of-thumb for specifying machining process, grinding's principal advantage is still its ability to create geometric features to single-digit micron tolerances and surface finishes to submicron specifications. Today's turning and other machining technologies have difficulty holding those tolerances and creating such finishes, especially on high-production lines.

Of course, grinding is no different than other machining methods in that surface finish and dimensional tolerances suffer as the material-removal rate increases. Grinding, however, retains its advantage in holding tight tolerances and leaving fine finishes throughout its new range of cutting speeds. Surface finish might be rougher and tolerances looser in a green-roughing operation, but they are typically better than those produced by a turning or milling operation. …

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